The invention relates generally to a snow vehicle and, more particularly, to a cycle type snow vehicle designed for banked turning, and to conversion kit assemblies used to convert a two-wheeled land vehicle such as a motorcycle or bicycle into a vehicle suited for over-snow travel.
A variety of vehicles have been designed for travel over snow, with the well known snowmobile type being by far the most prevalent and commercially successful. Snowmobiles have evolved into highly refined and capable vehicles for travel over snow and are used predominantly for recreation. Yet, these commercially available snowmobiles exhibit a number of undesirable features and characteristics that limit their agility and versatility. They are generally quite heavy, weighing typically from 400 to 600 pounds, and require powerful motors to provide power-to-weight ratios sufficient for high performance in highly variable power-sapping snow conditions and for the wide furrows they plow through the snow. A snowmobile typically has two outboard steering skis and a relatively wide, flat track. The outrigger positioning of the skis and the wide flat track constrain the snowmobile to travel flat upon the snow and inhibit banked or leaned turning. These features also tend to limit the steepness of slope that the snowmobile can traverse, since the snowmobile can easily slide sideways when traveling across a steep slope. When cornering on hard packed snow, a snowmobile cannot be easily banked to achieve tight-radius cornering, and the operator must move his or her body far to the inside of the turn to avoid tipping or side slipping the snowmobile.
A second much less common type of snow vehicle is the snow bike or snow cycle. These vehicles are generally smaller and lighter than snowmobiles. Snow cycle designs are usually based upon off-road motorcycles or scooters with the front wheel replaced by a ski and the rear wheel replaced by an endless loop traction belt, commonly called a track. Snow cycles are vehicles designed for banked turning like a motorcycle or bicycle, and are operated xe2x80x9cin balancexe2x80x9d. Snow cycles typically have a single steering ski and a relatively narrow track located behind and in line with the single ski. In turns, a snow cycle is leaned sideways in the direction of the turn such that the sum of gravitational and centrifugal forces acting on the vehicle and operator bears centrally on the contact areas between the snow and the ski and between the snow and the track. In this way, the snow cycle and rider remain in balance through the turn. When traversing slopes, a snow cycle maintains a vertical position such that the gravitational forces acting on the snow cycle and operator intersect the approximate center of the contact areas between the snow cycle ski and the snow and between the track and the snow.
Motor-driven snow cycles are described in U.S. Pat. Nos. 5,474,146, 4,613,006 and 4,442,913. None of these snow cycles have achieved notable commercial success. The snow cycles described in the ""006 and ""913 patents have minimal suspension travel between the ski and the vehicle main frame and between the track support and the main frame. The ability of their tracks to incline and decline relative to their front skis is also limited, reducing the compliance of their tracks to varying terrain and limiting traction. While the snow cycle described in the ""146 patent exhibits improved suspension travel and traction over the earlier snow cycles, it does so by using a track carriage that extends rearward from the snow cycle, making the snow cycle longer than the snow cycles referenced in the ""006 and ""913 patents. Positioning the track so far rearward from the snow cycle center of gravity limits the braking effectiveness of the track for slowing and stopping the snow cycle.
Human powered snow cycles or xe2x80x9csnow bicyclesxe2x80x9d are also banking snow vehicles. In snow bicycles, a single ski in front and an endless-loop track in back replace the bicycle wheels. Drive power from the operator""s legs is transferred from a pedal crank through a chain and sprocket drive train to the track. Snow bicycles are described in U.S. Pat. Nos. 5,423,559 and 5,102,153. The vehicles described in these patents exhibit all of the same limitations as conventional motor driven snow cycles. In addition, the absence of shock absorbers or some other type of suspension between the tracks and the frames of these snow bicycles limits traction and results in an uncomfortable ride over rough terrain.
Many conversion kit snow vehicles have been conceived that allow a motorcycle or motor scooter to be adapted to over-snow use by removing the wheels and attaching one or more skis in place of the front wheel and one or more tracks in place of the rear wheel. The tracks of these converted vehicles are driven from the engine and transmission of the motorcycle or motor scooter. Some of these converted snow vehicles use two side-by-side tracks outboard of the sides of the motorcycle, and ride flat upon the surface of the snow, with the motorcycle frame remaining perpendicular to the surface of the snow. Examples of this type of conversion kit snow vehicle are described in U.S. Pat. Nos. 3,667,562 and 3,822,755. These converted snow vehicles are generally quite heavy with very limited cushioned suspension travel between their frames and their tracks. The outrigger positioning of their dual tracks constrain the converted snow vehicle to travel with both tracks flat upon the snow, and prevent leaning of the vehicle in turns as can be done with a snow cycle. Conversion kits for converting a motorcycle or motor scooter for over snow use as a banking snow cycle have been described in U.S. Pat. Nos. 4,488,616 and 4,719,983. These conversion kits comprise small track carriages that are attached to the motorcycle or motor scooter frames and located below the rear wheels. Their track belts encircle the track carriages and the rear wheel of the motorcycle or motor scooter engages separate wheels or gears that, in turn, engage the outer surface of the upper run of the track to propel the converted snow vehicle. These conversion kits add significant weight to the host motorcycle or motor scooter. The track carriage of the conversion kit described in U.S. Pat. No. 4,719,983 mounts at its forward end directly to the frame of the motor scooter, preventing cushioning between the track carriage and the motor scooter frame. None of these conversion kits have achieved any notable commercial success.
The present invention is directed to a kit of component assemblies that in combination with a motorcycle chassis and engine form a cycle type snow vehicle that offers improved agility and maneuverability in snow conditions ranging from powder snow to hard packed snow and ice and over varying terrain topography. The converted snow cycle is designed to emulate the steering and balancing characteristics of motorcycles and bicycles to make the converted snow cycle easier and more natural for the operator to ride and control. Unlike conventional snow cycles that deliver power to the front of the track, the conversion kit-adapted snow cycle of the present invention delivers power to the back of the track. The track extends forward from the track drive wheel to position the track substantially under the snow cycle for improved propulsion and braking traction. The scissors-type configuration of the swing arm and track also helps reduce the overall length of the snow cycle. A novel track carriage suspension improves tractional compliance of the track to the snow surface over varying terrain topography. The track design utilizes a flat belt to enhance edging and support in soft snow. Traction paddles that are quite stiff with paddle tips having laterally convex curvature are deployed to allow the snow cycle to be easily leaned or banked on hard packed snow or ice.
The snow vehicle conversion kit of the present invention includes a track assembly that includes a suspension arm, a track carriage, and a power drive train. It also includes a ski steering member having an upper portion configured for attachment to the front fork of the host motorcycle or bicycle and a lower portion mounting a ski. The forward portion of the track assembly suspension arm is configured to be adaptively mounted to the motorcycle or bicycle frame. The rearward portion of the track carriage is mounted to the rearward end of the arm. A rotatable drive wheel is mounted to the rearward portion of the track carriage. The track is coupled to and extends forward from the drive wheel and circulates in a fixed path around the track carriage. In the motorcycle conversion kit embodiment, the track assembly includes a power drive train to couple the motorcycle motor to the drive wheel to drive the track and propel the vehicle over the snow. In the bicycle conversion kit embodiment, the conversion kit track assembly includes a power drive train for coupling the bicycle""s pedal crank to the drive wheel for human-powered propulsion of the converted bicycle over the snow.
In one embodiment of both the motorcycle conversion kit track assembly and the bicycle conversion kit track assembly, the track suspension arm is a swing arm that is configured to form a pivotal hinge attachment at its forward end to the main frame of the motorcycle or bicycle. The back of the track carriage is hinge mounted to the rear of the swing arm. This hinged mounting is implemented, for example, by an axle that extends between the prongs of a forked swing arm. The rear of the track carriage and the drive wheel are supported on the axle. This hinge mounting and positioning of the track carriage beneath the swing arm in a scissors-type configuration enables the track carriage to move vertically under the converted snow cycle, and allows the track carriage to incline and decline to follow the snow surface to maintain traction upon the snow. In one version of this embodiment, the combined mass of the converted snow cycle and operator is cushioned upon both the front and back of the track carriage by a single shock absorber combined with a force-distributing bell crank. The force-distributing bell crank distributes the vehicle suspension force from the shock absorber to the back of the track carriage through the swing arm and to the front of the track carriage through a connecting rod. Additionally, the bell crank can pivot to allow the track carriage to incline and decline without a change in the force exerted upon the bell crank pivot by the shock absorber.
The track assembly optionally has a snow compacting ramp is attached to the front of the track carriage positioned forward of the track and inclined upward away from the track to progressively compress the snow ahead of the track for improved traction and to prevent snow from packing in front of the track. One embodiment of the ramp assembly utilizes a ramp frame that is rigidly mounted to the track carriage frame and holds the snow ramp in a fixed attitude relative to the track carriage. A second embodiment of the snow compacting ramp has a ramp frame that attaches pivotally at its rearward end to the forward portion of the track carriage and is suspended from the motorcycle frame at its forward end. This is accomplished, for example, using a pair of swing pivot links that connect between the forward end of the ramp frame and a ramp pivot bracket that attaches to the bottom of the motorcycle frame.